Above all, inkjet technology has remarkable features of compactness and low power consumption as a direct recording method. In addition, enhancement of image quality has been rapidly advanced by miniaturization of nozzles, and so on. An example of the inkjet technology is a method of forming an image on a recording medium by heating ink supplied from an ink tank by heaters in nozzles so as to be evaporated and to form bubbles therein to discharge ink therefrom. As another example, there is a method of discharging ink from nozzles by vibrating piezoelectric elements. In addition, in these methods, improvements have been desired in terms of bleeding and feathering. For the improvements thereof, U.S. Pat. No. 5,085,698 discloses the use of pigment-dispersed ink.
Furthermore, for manufacturing ink compositions and toner compositions, in many conventional cases, coloring materials have been dispersed in solutions in which binder resins are dissolved. As the binder resins generally used for a wet dispersion of pigments, for example, styryl, acryl, and methacryl polymer compounds have been used. However, for preparing pigment ink in which a solvent, particularly water, is used as a base material, it is preferable to use a polymer material having an ionic functional group.
On the other hand, a polymer compound having a polyalkenyl ether main chain is also known as a polymer material having a flexible polymer chain, an ionic functional group has been hardly introduced in the repeating unit of a polymer compound. Barely, carboxylic acids and esters thereof are described as possible materials in “Journal of Polymer Science Part A Polymer Chemistry” vol. 27; pp. 3303-3314, 1989, and in the present circumstances, more stable polymer compounds have been desired.